1. Field of the invention.
The present invention relates to pipe float valves for use in lowering casing or drill pipe into a borehole in a rotary well drilling operation.
Float valves are ordinarily installed in the lowermost portion of a well casing string or the drill collar section immediately above a rotary drill bit. When used with drill collars the lower end portion of the drill collar bore is diametrically enlarged to accommodate the float valve which is held in place by the drill bit and accommodates the vertical reciprocating action of the valve in the float valve.
Float valves, as used with well casing and drill pipe, form several functions, such as providing a circulation path for well fluids from the casing or drill pipe to the annulus therearound; prevents back flow from the annulus into the casing or drill pipe of well fluids including displaced cement in a casing cementing job; provides a measure of blow-out prevention; and, floats the casing or drill pipe into the borehole thus using buoyancy to lighten the traveling block load and mass of the casing or pipe on the derrick. Additionally, the float valve, when operating properly in a drill pipe string, releases the drilling mud in the drill pipe borehole as the drill pipe is progressively removed from the borehole thus eliminating a spilling of drilling fluid on the rig floor and the workmen when pulling the drill pipe to replace the drill bit. A nonreturn check-type float valve is essential in all of the above described operations.
2. Description of the prior art.
The presently known and used casing and drill pipe float collars or valves usually comprise three types, a flapper or swing flap-type, a ball valve and a plunger valve.
The flapper in the flap-type valve is horizontally hinged for vertical pivoting movement and normally biased toward a closed position by a torsion spring offering a minimum resistance to flow.
The ball type float valve employs a cage and a free ball, as its closure element. The body of the valve is of two piece construction, one piece providing a sealing surface for the ball valve and a ball retention construction in the other portion. The ball valve is not normally spring loaded but may include an elastomer seal, the ball being biased by gravity to open position with resistance to flow being somewhat higher than the flapper valve.
The plunger type float valve is generally preferred and is superior in operating characteristics. The valve body provides a stop and seat for a valve stem mounted conical-shape valve spring biased closed by a compression spring surrounding the valve stem in which an elastomer surface insures a seal. This valve is opened by fluid flow forces in the free flow direction with movement of the plunger axially from its seat with the actual opening travel depending on the fluid flow forces and the spring constant.
The flapper valve offers substantially no constriction to flow while the ball and plunger types are approximately equal in pressure drop or obstruction to flow and are slightly higher than the flapper type. The contaminated-fluid resistance of the three valves are approximately equal. The flapper valve is capable of passing larger pieces of contaminant and all three types can be held partially open by contaminant trapped between the closing valve and the body or its seat, such leakage ultimately results in a cutting action and permanent damage to the valve.
U.S. Pat. No. 2,858,838 is an example of the presently used plunger type float valve which, as mentioned above, is the generally preferred float valve. The principal objection to the plunger type float valve is that in the open fluid passing position the well fluid under pump pressure generates angular rotation of the conical-shaped valve and its axial stem or shaft. Such rotation results in excessive wear on the valve stem and its sleeve-like valve stem guide which results in out of axial alignment of the valve and a failure to seal with its seat when biased toward a closed position.
This invention is an improvement over the plunger type float valve by providing means for arresting angular rotation of the valve in the float valve when in open position.